1. Field of the Invention
The present invention relates to telecommunications and, more particularly, to a method of requesting a communication session, such as a “push-to-talk” (PTT) session, using segmented signaling messages.
2. Description of Related Art
Mobile stations are increasingly being used to send and receive real-time media, such as voice and/or video, in a packet-data format. For example, a mobile station may use the Real-Time Transport Protocol (RTP) to send and receive such packetized media.
In order for a mobile station to establish RTP communication with an endpoint, the mobile station may engage in signaling, for example, using the Session Initiation Protocol (SIP). To request a communication session, the originating mobile station may send to a SIP proxy server a SIP INVITE message that designates a terminating endpoint, e.g., a destination mobile station. The INVITE may include a Session Description Protocol (SDP) block that characterizes the proposed session as an RTP session. The proxy server may then query a SIP registry to determine an IP address of the destination mobile station. The proxy server may then forward the INVITE to that address. The destination mobile station may agree to establish the session by sending a SIP 200 OK message via the proxy server to the originating mobile station. The originating mobile station may then send a SIP ACK message via the proxy server to the destination mobile station. At that point, the originating mobile station and destination mobile station may begin to communicate RTP packets with each other.
The originating mobile station may also be able to establish the session through a media server. The media server may function to set up respective RTP sessions or “legs” with the originating mobile station and one or more destination mobile stations. The media server may also conference the various legs together.
A wireless service provider may establish sessions through a media server in order to provide a “Push-to-talk” (PTT) service that simulates the experience of two-way radio communication. For example, a PTT-capable mobile station may include a button or other mechanism that the user can actuate in order to initiate a PTT session with a designated group of one or more other users. When the user presses the PTT button, a PTT client application in the mobile station may responsively send an INVITE message to a proxy server. The proxy server may then forward the INVITE message to a PTT server, e.g., a media server that runs a PTT application.
The INVITE message may identify a “communication group” for the user, i.e., a group of other users with whom the initiating user would like to communicate. The PTT server may then set up RTP legs with the initiating user and with each member of the group. The PTT server may then conference the RTP legs together so as to allow the members of the group to communicate with each other and with the initiating user.
Latency can be a problem with this approach, however. For example, a period of several seconds may pass after the user of the originating mobile station presses the PTT button before the PTT session with the designated group is fully established. This several second delay can result from a number of factors including (i) the time it takes for the originating mobile station to acquire a radio link and/or data link so as to be able to transmit the SIP INVITE message; (ii) the time it takes for the SIP INVITE message to propagate to the destination mobile stations; (iii) the time it takes for each destination mobile station to respond to the SIP INVITE message, e.g., with a 200 OK message. In addition, if a destination mobile station is in a dormant state, then additional time is required for the destination mobile station to acquire a radio link to receive the SIP INVITE message.
Accordingly, there is a need to provide methods for reducing the time it takes to establish communication sessions.